tst: Provide test for ctime

This change adds new test to assess ctime's functionality.

To be more specific - following use cases are checked:
- Pass time_t value as 0 to check if epoch time is converted
- Pass time_t as max value for 32 bit systems
- Pass time_t as the first value after Y2038 threshold

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

2 files changed, 57 insertions, 1 deletions

diff --git a/time/Makefile b/time/Makefile
index 347f94c..2dd7011 100644
--- a/time/Makefile
+++ b/time/Makefile
@@ -48,7 +48,7 @@ tests	:= test_time clocktest tst-posixtz tst-strptime tst_wcsftime \
 	   tst-strptime3 bug-getdate1 tst-strptime-whitespace tst-ftime \
 	   tst-tzname tst-y2039 bug-mktime4 tst-strftime2 tst-strftime3 \
 	   tst-clock tst-clock2 tst-clock_nanosleep tst-cpuclock1 \
-	   tst-adjtime
+	   tst-adjtime tst-ctime
 
 include ../Rules
 
diff --git a/time/tst-ctime.c b/time/tst-ctime.c
new file mode 100644
index 0000000..e89a906
--- /dev/null
+++ b/time/tst-ctime.c
@@ -0,0 +1,56 @@
+/* Test for ctime
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <time.h>
+#include <stdlib.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  char *str;
+  time_t t;
+
+  /* Use glibc time zone extension "TZ=:" to to guarantee that UTC
+     without leap seconds is used for the test.  */
+  TEST_VERIFY_EXIT (setenv ("TZ", ":", 1) == 0);
+  tzset ();
+
+  /* Check if the epoch time can be converted.  */
+  t = 0;
+  str = ctime (&t);
+  TEST_COMPARE_STRING (str, "Thu Jan  1 00:00:00 1970\n");
+
+  /* Check if the max time value for 32 bit time_t can be converted.  */
+  t = 0x7fffffff;
+  str = ctime (&t);
+  TEST_COMPARE_STRING (str, "Tue Jan 19 03:14:07 2038\n");
+
+  /* Check if we run on port with 32 bit time_t size */
+  time_t tov;
+  if (__builtin_add_overflow (t, 1, &tov))
+    return 0;
+
+  /* Check if the time is converted after 32 bit time_t overflow.  */
+  str = ctime (&tov);
+  TEST_COMPARE_STRING (str, "Tue Jan 19 03:14:08 2038\n");
+
+  return 0;
+}
+
+#include <support/test-driver.c>